Doherty amplifiers are used conventionally to set up high-frequency amplifiers with high efficiency and high linearity.
A Doherty amplifier which uses a 3 dB coupler simultaneously as an impedance transformer for the main amplifier and as a power combiner for the main and auxiliary amplifier by terminating the de-coupled terminal of the 3 dB coupler, which is normally terminated with the system wave impedance, with a short-circuit or open-circuit line of a given length, is known from European Patent EP 1 609 239 B1. The arrangement shown in that context has the disadvantage that a frequency variation beyond the conventional Doherty bandwidth is not possible, and the space requirement for a low-loss line is relatively large.